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dm bufio: avoid a possible ABBA deadlock

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commit 1b0fb5a5b2dc0dddcfa575060441a7176ba7ac37 upstream.

__get_memory_limit() tests if dm_bufio_cache_size changed and calls
__cache_size_refresh() if it did.  It takes dm_bufio_clients_lock while
it already holds the client lock.  However, lock ordering is violated
because in cleanup_old_buffers() dm_bufio_clients_lock is taken before
the client lock.

This results in a possible deadlock and lockdep engine warning.

Fix this deadlock by changing mutex_lock() to mutex_trylock().  If the
lock can't be taken, it will be re-checked next time when a new buffer
is allocated.

Also add "unlikely" to the if condition, so that the optimizer assumes
that the condition is false.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mikulas Patocka 2017-04-30 17:33:26 -04:00 committed by Greg Kroah-Hartman
parent 4df4bf1df9
commit 5d1df36c9d
1 changed files with 5 additions and 4 deletions
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9
drivers/md/dm-bufio.c
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@ -914,10 +914,11 @@ static void __get_memory_limit(struct dm_bufio_client *c,
{
unsigned long buffers;
if (ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch) {
mutex_lock(&dm_bufio_clients_lock);
__cache_size_refresh();
mutex_unlock(&dm_bufio_clients_lock);
if (unlikely(ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch)) {
if (mutex_trylock(&dm_bufio_clients_lock)) {
__cache_size_refresh();
mutex_unlock(&dm_bufio_clients_lock);
}
}
buffers = dm_bufio_cache_size_per_client >>